The comparative parliamentary stability which Sri Lanka has been experiencing in the last three decades has been attributed to the strength of the country's political system. Some observers refer to “the survival of something close to a two-party parliamentary system, where the two major political parties, more often in association with the fragmented Left and the disintegrating commimalist forces, compete for political power.”1 The electoral changes in the period 1956–77 explain the existence of a two party system unique in character; it was this phenomenon which assisted in the working of a comparatively stable political system in the island. Despite the divergent ideologies which the political parties professed, they perhaps were committed to the orthodox characteristics of the Westminster model. Marxists were even more adamant than their political enemies in insisting on the observance of the rules, procedures and conventions of the parliamentary game of politics.2 The 1977 electoral change and the subsequent political developments brought about a decline in the system of parliamentary government in Sri Lanka. The dim of this essay is to substantiate this view.